For now, I have the same modem and I use a cradlepoint 350 router.

http://www.evdoforums.com/viewforum.php?f=26

(their beta version available from 3gstore/evdoinfo supports the UM150, but they should have a new release soon)

1. It is properly recognized with the cdc_acm.ko kernel module.
2. The microSD works just like a thumbdrive or similar and will mount FAT/FAT32 media.
3. Either way it requires a powered hub and something (like an adapter with pins 4 and 5 shorted) to go into host mode.
4. lsusb, or pppd will eventually crash the USB subsystem due to a phantom endpoint causing a null pointer dereference. Reboot required for USB to recover. This does not appear to be the cdc_acm driver but the /sys/usb stuff (which is used instead of /proc/bus/usb so my Ubuntu Laptop doesn't easily duplicate the condition).
5. That said, I do get the IP address and DNS values, so as soon as I can figure out the more general USB problem, I won't need the router. Only when the data is blasted over the bus does the hiccup happen.